In the past there has been a demand for techniques by which facsimile printers, copiers and television images etc. can be recorded in color. Color recording techniques using electrophotography, ink jets and heat sensitive transfer etc. have been investigated for this purpose.
The heat sensitive copy recording system is such that the equipment is easy to maintain and operate, and the equipment and consumables therefor are cheap. Thus, it is thought to have an advantage over the other methods listed above.
Heat sensitive copying systems include (1) fusion systems which employ a transfer sheet, in which a layer of ink which can be melted by heating is formed on a base film, is heated using a heat sensitive head so that the ink is melted and a copy is recorded on the object on which the recording is to be made; and (2) sublimation systems which employ a transfer sheet, in which an ink layer which contains a sublimable dye has been formed on a base film, is heated by a heat sensitive head so that the dye sublimes and a copy is recorded on the object on which the recording is to be made. It is possible to control the extent of the sublimation of the dye by varying the energy which is supplied to the heat sensitive head in the case of the sublimation system. Thus, with this method, it is easy to achieve graded recording, a particular advantage for full color recording.
Dyes which are to be used in such a recording system must satisfy the following conditions: (1) the dyes must sublime easily under the operation conditions of the heat sensitive recording head, (2) the dyes must not be thermally degraded under the operating conditions of the heat sensitive recording head, (3) the dyes must have the hue preferred from the point of view of color reproduction, (4) the dyes must have a large molar extinction coefficient and be stable with respect to heat, light, humidity and chemicals etc., (5) the dyes must be easily prepared, and (6) the dyes must be suitable as inks, etc.
The dyes which have been suggested in the past, for example the anthraquinone dyes, naphthoquinone dyes etc. disclosed in JP-A-60-151097 and JP-A-60-151098 etc. have a poor hue, and the indoaniline dyes disclosed in JP-A-61-22993 have the disadvantage of poor heat resistance and light resistance. (The term "JP-A" used herein means an "unexamined published Japanese patent application".)